This invention relates to a method of forming a fluorescent screen for a color picture tube using photosensitive material which exhibits stickiness when exposed to light.
There have been proposed such methods as photographic method or printing method for forming a fluorescent screen for a color picture tube. Among them, the photographic method has been most preferred for use in mass-production. As well known in the art this photographic method is based on the utilization of photoresist and carries out formation of a fluorescent screen of triads of phosphors of primary colors, red, blue and green, in the form of dots or stripes on the inner surface of the panel by repeating exposing and developing steps.
Conventionally, for forming the fluorescent screen, there have been availed various methods, of which one uses a mixture of phosphor material, photosensitive agent and water which is in the form of slurry (referred to as slurry method hereinafter) and another, proposed by the same applicant as the present application, uses a material which becomes sticky by photo-exposure (referred to as dry method hereinafter). The former, slurry method uses a larger amount of solution than the latter, dry method. Therefore, the latter is superior to the former as regards to the mass-producibility. This invention is involved in the field of the latter dry method. One may refer to Japanese patent application laid-open No. 126861/'78 as an article disclosing the dry method.
The dry method of forming a fluorescent screen comprises forming a photosensitive film on the inner face of a panel which becomes sticky when exposed to light; attaching a mask with apertures of a predetermined pattern, such as a shadow mask, to the interior of the panel; exposing to light locations at which a phosphor material of a first color, for instance, blue, should be coated; removing the shadow mask; spraying phosphor powder of blue color on the panel inner face; and fixing the phosphor materials only on the locations which have become sticky. The shadow mask is attached again to the interior of the panel under this condition, and locations of the photosensitive film on which a phosphor material of a second color should be coated are exposed to light by, for example, displacing a light exposure source. The shadow mask is removed after making the location sticky and the phosphor material of the second color, for instance, phosphor powder of green color is sprayed on the inner face of the panel to be fixedly attached to the locations which exhibit stickiness. A similar process is repeated for a third color, thereby forming a predetermined pattern of triads of phosphor materials. Thereafter, known filming, metal backing and bakeing processes are carried out to complete a fluorescent screen.
The method to form the fluorescent screen described above requires to mount and dismount the shadow mask for three times for the formation of the pattern of each color. The shadow mask, though easily deformable, is required to be of high precision. Therefore, such repeated mounting and dismounting is not desirable both quality-wise and process-wise. As a countermeasure to solve such a problem, automatic mount and dismount of the shadow mask may be availed, which is satisfactory to guarantee quality of the fluorescent screen and has many difficulties with reliability and economy of the automated system itself.